The invention relates generally to systems for monitoring a medical patient's condition, and more particularly to monitoring systems including a moisture trap for removing moisture which has condensed from a patient's exhalation.
In the course of medical treatment, it is often desirable to monitor a patient's exhalation and, in some instances, analyze its gaseous composition. This may be monitoring, for instance, for apnea or analyzing the exhalation of a patient under anesthesia. Typically, the patient's exhalation is monitored by transferring a portion of the patient's exhalation to a suitable sensor.
Accurate analysis of the gases in a patient's exhalation depends upon the collection of the flow of exhalation without the introduction of factors which might distort the results of the analysis. Introduction of contaminants into the flow, or other alteration of the exhalation in the monitoring system, can render analytical results which do not reflect the actual condition of the patient.
Because a patient's exhalation is usually relatively humid, moisture must be removed before the sensor. Moreover, water can condense as the exhalation flows from the patient to the sensor. This then identifies two possible sources of moisture contamination, i.e., entrainment in the exhalation per se and re-entrainment of prior condensation into a subsequent stream of exhalation. Condensation can result in inaccurate readings at the sensor. In addition, collected condensation can interrupt the smooth flow of exhalation to the sensor, another possible distortion of the sensor operation.
Also, sensing devices used in patient monitoring systems, such as an infrared spectrometer, are often delicate and can be uncalibrated by moisture entering the sensor.
In order to remove moisture from the exhalation to prevent distortion of the gaseous composition of the exhalation and to protect the sensing devices, it has been known to place a moisture trap between the patient and the sensing device to separate moisture from the exhalation before it enters the sensing device.
Some prior art moisture trap designs utilize a porous, hydrophilic material to separate water vapor from a flow of exhalation. While hydrophilic materials can effectively remove a quantity of condensed moisture from a flow of humid gas, their use in some prior moisture trap designs have introduced other problems. More specifically, hydrophilic materials are porous and include voids. Such prior art moisture tap designs using hydrophilic materials remove moisture from the exhalation by allowing the exhalation to pass in proximity with or through the hydrophilic material. These arrangements can alter the gaseous composition of the exhalation being monitored by allowing gases held in the porous hydrophilic material to become re-entrained with and mix with the flow of exhalation. More specifically, this could be in the form of previously exhaled air or sample gas which had been held in the voids and which is later released into a subsequent stream of exhaled air or sample gas, thereby distorting the gas content of that subsequent stream such that when the stream reaches the sensor, it is not an accurate representation of the patient's condition at that instant. The greater the volume of hydrophilic material exposed to the flow of exhalation, generally the greater volume of gas which can be stored therein and then be available to later contaminate the exhalation. Minimizing the volume of hydrophilic material used in some prior art designs can decrease the amount of such mixing, but can also undesirably decrease the capacity of the moisture trap.
It is an object of the invention to provide a moisture trap for removing condensed moisture from a flow of exhalation without altering the gaseous composition of the exhalation.
It is a further object of the invention to provide a moisture trap having an expanded capacity to absorb condensed moisture from a patient's exhalation which assures that moisture will not pass through the moisture trap and into the sensor thereby protecting the sensor.
Among the more specific objects of this invention is to provide a moisture trap which provides a smooth flow of exhalation from the patient to the sensor in a fluid flow sense, while achieving increased moisture separation and minimizing the possibility of entrainment and contaminants in a given stream of exhalation.
Yet another specific object of this invention is to effectively interrupt the flow of exhalations when the moisture trap becomes saturated and can no longer effectively separate moisture from the exhalation.